This invention relates to a carbon monoxide sensor material and to a method of detecting carbon monoxide in a gas.
It is known that a metal oxide film of a positive-type semiconductor, such as a nickel oxide (NiO) film or a cobalt oxide (Co.sub.3 O.sub.4) film, can absorb light with a wave length of 350-1,500 nm when contacted with an oxygen-containing gas at an elevated temperature. When a reducing gas such as carbon monoxide is present in the gas, the absorbance is reduced depending upon the concentration of the carbon monoxide. Thus, the metal oxide film might be used as a carbon monoxide sensor material. However, the sensitivity of the nickel oxide or cobalt oxide film to carbon monoxide is not good. Further, the response of such an oxide film to a change of the concentration of carbon monoxide is not fast. Therefore, the nickel oxide film and cobalt oxide film are not used in practice for the detection of carbon monoxide.